Smoke detectors powered from an alternating current line are inherently subject to failure if the line loses power. Battery powered detectors avoid line failure problems, have a naturally simple power supply which is adequate to energize LED light sources, and for these and other reasons are becoming desirable and advantageous. Battery life can be prolonged by energizing the light source periodically for short times by applying energy pulses to the source as shown in U.S. Pat. No. 3,846,773. But pulsing the light introduces the problem of distinguishing pulses of light scattered by smoke from pulses induced in the detector circuitry by electrical surges or noise spikes in external wiring or the environment. An additional problem is that a single induced pulse might trigger a false smoke alarm which cannot thereafter be terminated by the detector circuitry.
Accordingly one purpose of the present invention is to discriminate between noise spikes and smoke detection pulses in a pulsed, battery smoke detector of the scatter type. A further object is to provide control circuitry for the alarm which will terminate a false alarm initiated by noise. Yet another object is to employ a pulse generator both for energizing the light source and sounding an alarm in an intermittent mode distinct from that of the smoke alarm mode.